Ah, that fucking bolt. I just went through the same problem about a month ago. What it actually says in the haynes manual to do, is to wedge a screw driver into the flywheel to keep it from moving, and then using a large breaker bar. I assume that the motor is in the car, and the car is not on a lift. What me and my buddy did, was pry back the "dust shield" or whatever from the flywheel, put the car on 2 jack stands, take the tire off, front bumper off, and then I held the screw driver in with all my might, and he pulled on my bumper support and pushed with his feet on the crank pulley bolt with everything he had, and after a good 15 minutes of hell, we got it. This is also because my extensions bent when I had them on so that I could use a pipe extension, so he had to use his feet. Also, make sure you have a few 17mm sockets on hand, I ended up going down to Autozone and buying a set of impact sockets because my 3 craftsman 17mm's broke. You'll be kind of angry when you finally get it out though and realize how small of a bolt it is.
EDIT: This all is after going through the same problem you had for about 2 weeks, I don't know how many cans of WD-40 and liquid wrench I used on it, but it seemed to do nothing. Also, when you put it back in when putting it all back together, make sure you get some blue loc-tite and throw it on there.